A Novel Phase of Li15Si4 Synthesized under Pressure

Li 15 Si 4 , the only crystalline phase that forms during lithiation of the Si anode in lithium‐ion batteries, is found to undergo a structural transition to a new phase at 7 GPa. Despite the large unit cell of Li 15 Si 4 (152 atoms in the unit cell), ab initio evolutionary metadynamics (using the USPEX code) successfully predicts the atomic structure of this new phase (β‐Li 15 Si 4 ), which has an orthorhombic structure with an Fdd2 space group. In the new β‐Li 15 Si 4 phase Si atoms are isolated by Li atoms analogous to the original cubic phase (α‐Li 15 Si 4 ), whereas the atomic packing is more efficient owing to the higher SiLi coordination number and shorter SiLi, LiLi bonds. β‐Li 15 Si 4 has substantially larger elastic moduli compared with α‐Li 15 Si 4 , and has a good electrical conductivity. As a result, β‐Li 15 Si 4 has superior resistance to deformation and fracture under stress. The theoretical volume expansion of Si would decrease 25% if it transforms to β‐Li 15 Si 4 , instead of α‐Li 15 Si 4 , during lithiation. Moreover, β‐Li 15 Si 4 can be recovered back to ambient pressure, providing opportunities to further investigate its properties and potential applications.